This invention relates to a control device for controlling a battery charging AC generator driven by an internal combustion engine, and more particularly to a current limiting circuit disposed in a voltage regulator equipped with semiconductor devices.
When the storage battery is charged by AC generators driven by associated internal combustion engines, the AC output voltage therefrom is generally full-wave rectified and then controlled to a predetermined magnitude by a voltage regulator for stopping and causing the flow of a field current through the field coil thereof. Conventional voltage regulators have been comprised of the output transistor being serially connected to the field coil and subsequently connected to the storage battery, and the control transistor being responsive to the output voltage from an associated AC generator in excess of a predetermined magnitude so as to be conducting to thereby place the output transistor in its nonconducting state to break the field current. On the other hand, with the output voltage from the generator less than the predetermined magnitude, the control transistor is held in its nonconducting state to thereby place the output transistor in its conducting state to permit a flow of field current through the field coil.
Voltage regulators of the type as above described have disadvantages in that, upon the occurrence of an interphase shortcircuit in the field coil, a current flowing through the output transistor has a magnitude much higher than a permissible magnitude of the field current and a collector-to-emitter voltage thereof is also high resulting in the instantaneous breakdown of the output transistor because of a high power loss thereof.